Provider Backbone Bridges (PBB) are being defined by the IEEE 802.1 ah project to allow scaling of provider networks to 2024 (i.e., up to 16 million) “Service Virtual VLANs”. IEEE 802.1 ah adds the following fields to Ethernet frames transported through the PBBN (PBB Network):
B-DA: Backbone destination MAC address
B-SA: Backbone source MAC address
B-TAG: Backbone VLAN tag, which carries a backbone VLAN ID (B-VID)
I-TAG: Service Instance Tag, which contains a service instance ID (I-SID) identifying a service customer.
IEEE 802.1 ah specifies the Provider Bridge (802.1 ad) interface to a PBBN in terms of the operation and configuration of these fields.
IEEE 802.1 ah is also called MAC-in-MAC, since it keeps the original Ethernet frame and adds a new destination and source MAC addresses around the frame.
Provider Backbone Transport (PBT) is a variation on PBB that allows carriers to provision engineered and protected point-to-point service instances. PBT is intended to make Ethernet point-to-point transport more attractive to operators that are used to SONET/SDH networking, potentially positioning PBT Ethernet systems as a longer-term replacement for SONET/SDH.
PBT operates by adding configured routes to a PBBN. Each PBT trunk forwards on a 60 bit field composed of the B-VID and B-DA fields, and is identified by a 12 bit VLAN ID (B-VID) and a 96 bit source/destination address pair (B-DA, B-SA). A source of a PBT Trunk is identified by the B-SA and the destination of a PBT trunk is identified by the B-DA.
The interworking of PBT with services such as VPLS (Virtual Private LAN Service), EVPL (Ethernet Virtual Private Line), egress PBT trunks, connection to a Private IP network, connection to a Public IP Network (i.e., Internet), etc. is currently limited and improvements would be desirable.